Find all subsequence combinations of a string

Given a string 'abc', find all distinct subsequence combinations of it.

Hint

The algorithm breaks down the string character by character, starting from the end. At each step, it considers all the substrings found so far, and then creates new substrings by adding the current character to them. This process continues until all possible combinations are explored.

# Python implementation
def combine(s):
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// Javascript implementation
function combine(s) {
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